The present invention relates to shrouded turbine blades of the kind used in gas turbine engines. The invention has particular efficacy if used in gas turbine engines of the kind used to power aircraft.
During the operation of a gas turbine engine, combustion gases pass through a stage of guide vanes, and are directed thereby on to a rotary stage of turbine blades in a known manner. The stage of blades is thus rotated and, via connecting shafting, in turn, rotate a compressor and/or fan.
The side edges of the shrouds of the turbine blades are sealed one to the other, in known manner, by means which allows the blades to move away laterally from each other, under the influence of, inter alia, centrifugal forces, without producing gaps through which gases would escape. However, axial spaces must be provided between the downstream edges of shrouds surrounding the stage of guide vanes, and the upstream edges of the turbine blades shrouds, so as to avoid friction between the static and rotating stages.
During operational rotation of the stage of turbine blades, the rotational loads exerted on the gas flow, added to by the friction between the gas and the juncture of the blades aerofoil portions and their respective shroud under surfaces, causes the generation of a volume of relatively high pressure gas, which radiates outwardly of the blades surfaces, in directions other than in a downstream direction, but mainly in a direction forwardly of the blades leading edges, ie upstream, in the form of a jet. The force of the jet, under some operating regimes of an associated engine is sufficient to overcome the force of the gas leaving the corresponding area on the guide vanes, ie the juncture of their aerofoils and shrouds, in a downstream direction. There results an outwardly turned flow of gases through the gap between the guide vanes and turbine, which flow then reverses, to flow over the exterior of the turbine blade shrouds.
The present invention seeks to provide a shrouded turbine blade having improved gas flow control.
According to the present invention, a turbine blade comprises an aerofoil having a shroud on its radially outer end with respect to an axis of operation thereof, the leading edge of said shroud being locally shaped so as to at least substantially contain local gas flow which extends in directions other than downstream during in situ operation of said turbine blade in a gas turbine engine.